Dilatation catheter balloons are used in invasive medical procedures such as percutaneous transluminal coronary angioplasty (PTCA). This particular procedure has become a tool of major importance in the treatment of coronary heart disease, as described by D. S. Baim, MD, in Heart Disease. A Textbook of Cardiovascular Medicine. 4th Edition, Chapter 41, E. Braunwald, Ed, published by W. B. Saunders Company, 1992. A vascular stenosis is relieved by expansion of a dilatation catheter balloon which has been introduced into the occluded blood vessel at the site of the lesion by way of a catheter.
U.S. Pat. No. 4,490,421 (Levy) discloses high strength, high modulus biaxially oriented articles exhibiting a preferred mode of failure, the process being particularly well-suited for the production of dilatation catheter balloons for invasive medical procedures, as taught therein. It has been found in the practice of PTCA that a significant percentage of the stenoses relieved thereby are subject to restenosis, essentially a reversion to the previous occluded condition after removal of the balloon catheter. This may occur over a period of minutes, or may take weeks or months to occur. Increasingly, intraluminal prostheses known as stents are placed in the treated vessel to serve as a reinforcing member, and prevent the further accretion of materials at the location of the original lesion. Stents are for the most part made from metal wires or tubes. A preferred method for implantation of the stent is to place the stent around the outside of a balloon catheter. As the balloon is expanded to treat the lesion, the stent is simultaneously expanded. The balloon is subsequently deflated and withdrawn, leaving the stent in place.
During the dilatation procedure, the balloon is undesirably susceptible to puncture by the sharp edges of the stent during the expansion and implantation phase of treatment. A puncture so caused then induces a failure in the balloon, forcing the procedure to be aborted, thus subjecting the patient to unnecessary risk and adding undesirably to the cost of the procedure
It is known that improved puncture resistance of dilatation catheter balloons may be achieved by forming them from a coextruded tubular article wherein the inner layer is a polymer suitable for use as a dilatation catheter balloon, e.g., polyethylene terephthalate (PET), and a second layer is a more rubbery or so-called "toughened" composition affording improvements in puncture resistance. The tougher or more rubbery layer is resident on the outside of the catheter balloon, adjacent to the inside surface of the stent. For example, U.S. Pat. No. 5,290,306 discloses the use of a thermoplastic elastomer, of a hardness less than 55 D according to ASTM D2240, preferably a polyurethane, as the outer layer in a biaxially oriented coextruded tubular article wherein the inner layer is PET or polyamide. U.S. Pat. No. 5,195,969 discloses a biaxially oriented coextruded tubular article consisting of an inner layer of PET film and an outer layer of a so-called toughened blend of PET. These articles are said to exhibit improved puncture resistance.
It is thus highly desirable to provide a puncture-resistant dilatation catheter balloon suitable for use in PTCA accompanied by the implantation of vascular stents, and in other medical dilatation procedures.